Landfill design, construction, and operation are some of the most highly regulated activities in the United States. These activities involve federal, state and local regulations, all of which deal with the environmental impact of the landfill and its operation. Even the closure of a landfill is subject to strict regulations. Numerous permits must be obtained at virtually all levels of government. These regulations include provisions relating to groundwater quality protection; landfill gas control; air pollution; surface water discharge; flood plains; safety issues; settlement, slope stability; and basic operating procedures. Boundary and topographic surveys, hydrogeological information (e.g., geological formation, soil texture, structure, bulk density, porosity, permeability, moisture, ion exchange characteristics; depth and type of bedrock; groundwater depth, hydraulic gradients, and seasonal fluctuations); climatological data such as wind direction and temperature and other variables must be evaluated, measured and documented during design, construction and operation of a landfill.
Typically, landfills are constructed in phases or “cells” that are distinct hydraulic units. In landfill operations, the cell presently receiving waste is called the “working face” or “active area” of the landfill. As refuse is received at the working face it is dumped, spread and compacted in layers called “lifts”. Active areas are typically 200 ft×200 ft in size where a refuse compactor and/or a bulldozer are used to spread and compact refuse in lifts as it is dumped. The cell continues to be filled in lifts until it reaches capacity, at which time it is covered or capped. All landfills must have cohesive soil and/or synthetic liners at the bottom and along the sideslopes to isolate the refuse and contaminated liquid (or “leachate”) from the surrounding soil. Landfill cells can be classified as either “wet cell” or “dry cell” depending on how leachate is managed in the cell.
Moisture, such as rainfall, that enters landfill cells percolates through the refuse and produces leachate which accumulates at the lowest point of the cell bottom. This leachate is typically pumped and disposed of at a wastewater treatment plant or an in-house treatment system. In a dry cell, capping the landfill quickly with cohesive soil and/or synthetic barrier eliminates infiltration and ensures a relatively dry environment. The intent of operating dry cells is to minimize the amount of moisture entering the refuse mass and the subsequent amount of leachate formed.
Although wet cell landfills are known (as will be discussed more fully hereinafter), dry cells are more common. In dry cell landfills the deposited refuse dries and decomposes at extremely slow rates because moisture, an essential component of the decomposition process, is restricted. These dry cells are sometimes referred to as “Dry Tombs,” since it is not unusual for them to contain waste materials that have decomposed little after fifty years or more. Without decomposition, the landfill cells fill more rapidly and must be closed before their potential capacity is reached.
Conventional wet cells are those in which leachate generated in the landfill is collected and reintroduced into a cell, wherein the leachate is absorbed by and continues to percolate through the waste. This so-called “leachate recirculation” operation promotes biological decomposition of refuse. This approach differs greatly from the approach of dry cell management of solid waste landfills where, as stated, biological decomposition of waste is intentionally inhibited, by restricting the moisture content of the cell. In wet cell landfills, there is no need to prevent moisture from entering the cell. As the waste decomposes, it further compacts or consolidates, hence allowing additional refuse to be deposited into the cell. When these we cells are properly engineered and operated in a manner that maximizes decomposition and gas generation, they are sometime referred to as “landfill bioreactors” or “bioreactor landfills”.
Accordingly, it is evident that using landfill space efficiently and extending the site life to the extent possible, as well as recouping capital expenditure and operating the landfill profitably, are all desirable goals.
It is also known that septic systems separate the liquid of domestic sewage from solid and semi-solid materials by allowing these undissolved components to either settle to the bottom of a septic tank or float to the top while the liquid flows through a series of pipes that run to the soil absorption filed (a.k.a. the “septic field”). Thus, septic tanks collect settled and floatable solids from the wastewater. The septic field then filters and treats the partially clarified septic tank liquid and distributes it through the soil. The septic tank also promotes biological breakdown of a portion of the solids.
Periodically, depending upon a number of factors such as tank size and frequency of use, the contents of the septic tank (septage) must be removed from the septic tank. This is achieved by pumping the septage from the septic tank into a truck which hauls the pumped septage away from the site. Many septage haulers are small, independent companies. They typically dispose of the septage either at waste water treatment facilities or at sites permitted for land application. Wastewater treatment plants usually charge the haulers significant fees for disposal. Meanwhile, land application is inexpensive but the practice poses certain public health risks and increased regulation. It would be desirable to provide an alternative, environmentally safe and cost effective disposal for septage which could reduce the hauler's disposal fees and public health concerns.